A new technique has been conceived for measuring pulmonary parameters in non-cooperative subjects, particulary infants and children. Known vilumes of tracer gases are synchronously introduced into a nostril early enough in the inspirations to insure that all the tracer goes into the alveolar compartment. Alveolar gas is sampled during each expiration with a special automated gas sample. Using helium, acetylene, dimethylether, and Freon-12 as tracers, containuous monitoring of effective pulmonary blood flow, FRC, alveolar ventilation, O2 uptake, and CO2 production can be achieved. The method should be blind to left-to-right shunts, a hypothesis which will be tested in lambs with surgically induced ventricular septal defects. Measurement of VA/Qc imbalance is provided by the data from several soluble gases when applied to a multicompartment model. A portable unit will be built using a three channel gas chromatograph as the anaylzer, to provide sufficient sensitivity for measuring the low concentrations compatible with continuous breathing of the tracer gases.